The present invention relates to a toner collecting container for cleaning and collecting toner that remains on an image carrier after transfer of a toner image formed on the image carrier to a recording medium, a toner supply cartridge for storing fresh toner and supplying the same to the developing section of an image forming apparatus, and an image forming apparatus using the toner collecting container and the toner supply cartridge.
In image forming apparatus of the type utilizing electrophotography, usually, toner used for development of an electrostatic latent image formed on an electrostatic latent image carrier is mostly transferred to a recording medium and hence consumed for image formation, but partly remains on the electrostatic latent image carrier.
A very small amount of toner that adheres to a surface of the image carrier other than the electrostatic latent image region and is not transferred to the recording medium, also remains on the electrostatic latent image carrier. Other toner fractions that also remain on the electrostatic latent image carrier without being transferred to the recording medium include a toner fraction that is deposited on the image carrier surface during various image forming process steps, for example, a toner fraction that is used to form a reference density pattern on the electrostatic latent image carrier for the purpose of process control (image quality control) for maintaining a good image quality.
In attempt to reuse such residual toner effectively, methods have hitherto been proposed of collecting such residual toner remaining on the electrostatic latent image carrier into a developing device by collecting and transporting residual toner to the developing device with a cleaning device or by making the developing device perform a cleaning operation instead of such a cleaning device.
Such recovered toner, however, has such inclusions as foreign matters (including powdery paper, particles resulting from wear of power transmission members, dust and trash) and aggregates of toner. Further, it is possible that recovered toner has an undesirably reduced particle size as compared with fresh toner.
Further, it is possible that recovered toner becomes difficult to charge due to deterioration caused by being subjected to repeated image forming process, that a drop occurs in the friction-based charge carrying ability of recovered toner because of stress given by transfer charge or the like, that recovered toner contains reversely charged toner, or that a drop occurs in the fluidity of recovered toner, which is one of the physical properties of recovered toner.
It is therefore very difficult to use a mixture of recovered toner and fresh toner. With such a mixture, it is difficult to maintain uniformity in toner density and stability in the amount of electric charge carried by toner. When a large amount of recovered toner is supplied to the developing device at a time, it is possible that not a few toner particles adhere to a blank portion other than the image carrying portion of a paper sheet to stain the blank portion, thus degrading the image quality, or that the toner in the developing device becomes easy to scatter. To avoid such inconveniences, one known image forming apparatus is designed to dispose of collected toner without reuse (see Japanese Patent Laid-Open Publications Nos. HEI 4-208958 and HEI 6-258943 for example.)
In disposing of collected toner without reuse, however, a container dedicated to collected toner is required so as not to mix collected toner in fresh toner. Each of the apparatus disclosed in the aforementioned Japanese Patent Laid-Open Publications Nos. HEI 4-208958 and HEI 6-258943 has an integral structure comprising a collecting section for storing collected toner and a fresh toner storage section for supplying fresh toner to the developing section. With such an integral structure, it is difficult to determine the capacity ratio between the fresh toner storage section and the collected toner storage section. This is because the ratio of the amount of collected toner to the amount of toner used is not constant but greatly varies depending on operating states of image forming apparatus including, for example, an operating state where the image forming apparatus is operated frequently and an operating state where the image forming apparatus is operated occasionally. Particularly where toner is deposited on a surface of the latent image carrier to form a reference density pattern for the purpose of process control (image quality control) for maintaining a good image quality, the toner used is wholly collected and, hence, the amount of collected toner becomes considerably large when the frequency of image quality control is high.
Usually, image quality control includes forming a density patch image on the image carrier and then detecting this image. Based on the image thus detected, processing means associated with respective image forming process steps are controlled to maintain image formation of good quality. The image quality control is conducted taking account of the number of images having been formed so far, environmental conditions around the image forming apparatus, and like factors. Accordingly, the frequency of image quality control in the case of frequent image formation is higher than that in the case of occasional image formation.
Since toner used in image quality control is wholly collected into the collecting section, the amount of collected toner grows larger as the frequency of image quality control increases. For this reason, the capacity of the collected toner storage section needs to be set large enough, which results in an undesirably increased space required for the collected toner storage section. If the capacity of the collected toner storage section is relatively small, fresh toner still remains in the fresh toner storage section formed integral with the collected toner storage section when the collected toner storage section becomes fully filled with collected toner. As a result, there arises a problem that the integral toner storage device needs to be wholly replaced with a new one before the fresh toner in the fresh toner storage section is wholly used.
A feature of the present invention is to provide a developer storage device including a fresh toner storage section and a collected toner storage, which are independent of and removable from each other.